More commonly, non-traditional high temperature composite materials, such as ceramic matrix composite (CMC) materials, are being used in applications such as gas turbine engines. Components fabricated from such materials have a higher temperature capability compared with typical components, e.g., metal components, which may allow improved component performance and/or increased engine temperatures. Composite components may provide other advantages as well, such as an improved strength to weight ratio. Moreover, as gas turbine engine designers and manufacturers seek to further increase engine performance and efficiency, one known solution is to incorporate a counter-rotating turbine such that the turbine is vaneless. However, utilizing composite airfoils or blades in an interdigitated rotor assembly presents issues such as how to attach inwardly extending composite blades to an outer rotor (e.g., a rotating drum) without unduly increasing the thickness of the rotor, thereby increasing its weight, and with the capability to withstand stress concentrations at the attachment area. Nonetheless, such a configuration, which places the blades in compression rather than tension, benefits from the use of composite blades, e.g., CMCs have an increased modulus compared to metal that provides an increase in column buckling margin for blades run in compression.
Accordingly, a composite blade having features for attaching to a rotary structure, particularly of an interdigitated rotor assembly, would be useful. In particular, a composite blade that attaches to an outer rotor of an interdigitated rotor assembly in a manner that allows a minimal rotor thickness would be advantageous. Further, a composite blade with an attachment structure that minimizes stress concentrations at its area of attachment to an outer rotor of an interdigitated rotor assembly would be desirable.